The present invention relates to a load return mechanism for returning a load to a predetermined position upper power interruption and, more particularly, to a load return mechanism for returning a load to a predetermined position upon power interruption in which the motor driving the load does not have to operate against the load return mechanism during normal operation of the system.
In the control of various loads such as valves and dampers, it has become the practice to bias the load such that upon power failure the load will be driven to a predetermined position. Prior art arrangements merely relied upon a return spring for normally biasing the load opened or closed, whichever was preferred. However, whenever the actuator, such as a motor, operated the load to a different position, the actuator had to operate against the return spring. Thus, the size of the actuator necessary to operate successfully against the force exerted by the return spring on the actuator as well as the nonlinear relationship between the force that the motor had to exert against the spring as a function of the input to the motor both had to be considered. The present invention substantially eliminates force considerations while still providing a spring return to drive the load to a predetermined position upon power interruption or power removal.